/*
 * srm 166 div 2 prob 3
 */ 

import java.util.*;
import java.util.regex.*;
import java.text.*;
import java.math.*;


public class ConvexPolygon
{
    int[] x, y;
    int Area (int i, int j) {
	int x1 = x[i] - x[0], x2 = x[j] - x[0], y1 = y[i] - y[0], y2 = y[j] - y[0];
	return x1*y2 - x2*y1;
    }

    public double findArea(int[] x, int[] y)
    {
	this.x = x;
	this.y = y;
	int n = x.length;
	int area = 0;
	for (int i = 1; i < n - 1; ++i)
	    area += Area (i, i + 1);
	return Math.abs (area)/2.0;
    }
    
    <%:testing-code%>
}
//Powered by KawigiEdit 2.1.4 (beta) modified by pivanof!